1. Field of the Invention
The invention is directed to communication systems and, more particularly to a reservation map for frequency allocation in communication systems with transceivers operating as secondary users in a primary user frequency band.
2. Description of the Prior Art
Some radio spectrum licensees have a plurality of adjacent or disjoint radio channels or combinations thereof to support communication services such as, for example, analog voice services. Typically, user channel allocations will have standard bandwidths of 6.25, 12.5-, 25- or 50-kHz or multiples thereof. One concern of licensees is the efficient utilization of their aggregate bandwidth. In the example of analog push-to-talk voice services, some have chosen to use fixed-frequency or manual channelized radios. While these radios are inexpensive, they may offer poor utilization of the radio channels if they have a dedicated frequency or frequency pair; if the user only uses the radio ten-percent of the time, then ninety-percent of the user channels' bandwidth is wasted.
In another example, frequencies from different primary users are utilized harvested for use on a secondary use basis
In the above examples, additional radios could share the frequencies by using a “listen-before-talk” user discipline. This will improve the spectral efficiency but some users may have to wait until the frequency becomes clear or manually adjust the frequency if the radio has that capability and try again. Trunked radios offer an improvement over the mechanisms described above. Trunked radios signal a repeater station and the repeater will select a clear channel for the caller. There are several trunking protocols that can be selected, all of which share a disadvantage also shared by other push-to-talk mechanisms: the channelization of the radios is inflexible and efficiency of band usage may be low.
The radios described above and similar radios are inflexible in that they must be used only on a channel of fixed bandwidth (such as 12.5- or 25-kHz) and must remain on the same frequency throughout the duration of the session, making higher utilization of the bandwidth difficult. In addition, these radios do not easily allow additional services such as Ethernet and IP (Internet Protocol) digital services to co-exist and use the bandwidth when not used by the radios.
Problems of the Prior Art
A class of radios can receive multiple carriers simultaneously. In one example, a point-to-multipoint multicarrier master station radio can receive a data stream spread over the multiple carriers. A common problem in point-to-multipoint networks is how to share the band in the remote-to-master station direction (upstream). Various solutions for sharing the upstream bandwidth (“access method”) have been implemented, such as TDMA, Aloha, slotted Aloha, and many others.
All these access methods have some sort of implicit or explicit signaling. TDMA has implicit signaling in the fixed TDMA frame structure. The remote stations use the TDMA clock to identify which slots in the frame are available for each site, based on a slot-numbering scheme and a site-numbering scheme. In one form of slotted Aloha, the master station signals that a message was lost by sending ACK and NAK signals based on message sequence numbers. All such signaling schemes exact a cost on network throughput due to the signaling overhead and the effectiveness of the bandwidth-sharing scheme. The efficiency of the signaling scheme can be affected by many factors, including transit delay (especially satellite or low-speed networks), round-trip signaling delay, raw bandwidth overhead, interaction with higher-layer protocol timers and others. The cost of the sharing scheme comes in the form of some combination of throughput, jitter, delay and other factors.